Iris Mechanism Blades for 3d Printing
Ok. Actually, to model this blade, you have first to understand the underlying geometry. Its the intersection of 3 circles that make up that shape. In the following I will show you how to make that shape (with the hole) step by step.

EDIT:
0. go into Top Ortho by pressing Numpad 7


Create a circle with 30 vertices

Go into Edit Mode (press Tab) and make sure the circle is selected (if not press A until it is). Press Shift+D to duplicate the circle. Before confirming the action press Y and type in 1 to move the circle by one up.

Press . (not on your Numpad) to select Cursor Pivotcenter. Then press Shift+D again and this time press R and type in -72 to rotate your Circle correctly.

Next select the vertex at [0, 1, 0] (where the 3D Cursor is in the next image) and press Shift+S. Select Cursor to Selected in the popup menu. Your Cursor should now be where it is in the image. Then create a Circle by pressing Shift+A and make sure it has 6 vertices.

Activate the little magnet in the bar at the bottom of the 3D Viewport. Select Vertex in the combobox right next to it. Now press R and let the rotation snap in place exactly as shown in the image below. Then Confirm by LMB or Enter

Now Scale with S and let it snap to the same vertex. Again shown below.

Reset your Cursor to the Center py pressing Shift+S and selecting Cursor to Center. Make sure the setting with the magnet stayed the same and press R. Let the rotation snap in place like shown below and confirm.

Press S to scale and let it snap like shown below before confirming.

Select the vertices as shown in the image below and press Alt+M. Select At Center in the popup menu.

Next up you have to remove all temporary vertices. Make sure you are in Wireframe Mode (to the right of the Edit Mode combobox). If you are not in Wireframe Mode press Z to enter it. Press C to use the circle selection tool and select the vertices shown below. When finished press X and select Vertices to delete them.

Select everything whats left (press A until that is the case). Press W and select Remove Doubles. (In 2.8 press Alt+M and select By Distance)
Select the two vertices like shown below and press X and select Edges.

Select every vertex around the big face (every vertex except two which are part of the hexagon) and press F to make a Face. Select (only) the 6 vertices of the hexagon and press F. Then press I and adjust the size of the hole that you what to be in there. Then after you confirmed press X and Faces to make the hole.

The following part is completly optional and because you are a beginner it may be hard to do for you. In the picture below I made a beautiful topology to be used with the Subsurf Modifier. I made that mostly by using the Knife Tool (K). If you want you can copy my topology with that tool. The most important step here is to add the Edge Creases at the inner tip. Select the 3 vertices that are the closest to the 3D Cursor in the image and press Shift+E. Move your mouse until a Crease +1.000 appears in the bottom left corner of the 3D Viewport and confirm with LMB.

Press Strg+2 to add a Subsurf Modifier and exit the Edit Mode (Tab).

Add a Solidify Modifier in the Modifier Tab (shown in the image above) by clicking on Add Modifier and select it there. You can then Adjust the Thickness of the blade and Apply that modifier.
Enjoy tinkering